In recent years, due to an increasing interest in energy saving, there have been proposed many types of permanent magnet motors each of which uses a Nd—Fe—B rare-earth permanent magnet having a high residual flux density as a rotator, to thereby realize high efficiency.
In particular, as an electric motor for a compressor to be used in refrigeration equipment or air-conditioning equipment, an interior permanent magnet motor having a permanent magnet embedded in a rotator core is often used. In the rotator core, a plurality of magnet accommodating holes for embedding a plurality of permanent magnets are formed. In order to suppress electromagnetic exciting force generated at the electric motor, slits extended in a radial direction are formed in a core portion on an outer side of the permanent magnet.
For example, in a rotator of an interior permanent magnet motor disclosed in FIG. 2 of Patent Literature 1, a plurality of slits are formed in the vicinity of an outer peripheral portion of a core portion for a permanent magnet.
Besides, in some of the related-art electric motors, in order to operate an electric motor in a high temperature atmosphere of a compressor, much dysprosium (Dy) is added to increase J coercive force so that a rare-earth magnet is prevented from being demagnetized at high temperature. In particular, when an R32 coolant having a small global warming potential (GWP) is used, as compared to using a related-art 410A coolant, the temperature of the compressor is increased by 10° C. or more, and hence the addition amount of Dy is increased to increase the J coercive force.
For example, in a compressor disclosed in Patent Literature 2, a brushless DC motor and a compressor main body are concentrically arranged in a hermetically-sealed casing, a simple R32 coolant or an R32 rich mixed coolant is employed as a coolant to be taken, compressed, and discharged by the compressor main body, and J coercive force of a rare-earth magnet is set to 23 kOe or more.